Coal desulfurization process

ABSTRACT

COAL IS TREATED IN A REDUCING ATMOSPHERE IN A FLUID BED REACTOR TO PARTIALLY DEVOLATILIZE IT, REMOVE ALL MOISTURE, AND REMOVE SOME H2S AND SO2. THE THEN CHARRDD COAL IS TREATED IN A MULTI-STAGE CONTACTOR WITH HOT GAS COMPOSED OF HYDROGEN AND METHANE TO REMOVE MOST OF THE REMAINING SULFUR.

p 1973 c. M. WHITTEN ET AL 3,759,673

COAL DESULFURIZATION PROCESS 3 Sheets-Sheet Filed Nov.

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COAL DESULFURIZATION PROCESS Filed Nov. 5 1971 3 Sheets-Sheet 5 Q7 AP A? [7 United States Patent 3,759,673 COAL DESULFURIZATION PROCESS Charles M. Whitten, Columbia, and Vaughn Mansfield,

Gallatin, Tenn., and Louis J. Petrovic, Sudhury, and

Jagdish C. Agarwal, Concord, Mass, assignors to Peabody Coal Company Filed Nov. 5, 1971, Ser. No. 196,098 Int. Cl. C] 9/02, 9/08 US. Cl. 441 R 6 Claims ABSTRACT OF THE DISCLOSURE Coal is treated in a reducing atmosphere in a fluid bed reactor to partially devolatilize it, remove all moisture, and remove some H 8 and S0 The then charred coal is treated in a multi-stage contactor with hot gas composed of hydrogen and methane to remove most of the remaining sulfur.

BRIEF SUMMARY OF INVENTION H 8 to H may be as low as 1 to 100 and reach a low level of sulfur.

Exposure of coal to air oxidizing atmosphere during.

carbonization will remove substantially all of the pyritic sulfur in the form of S0 but then the remaining sulfur in the carbonized product is more diflicult to remove than if the product had been exposed to a reducing atmosphere during carbonization. Accordingly, treatment of coal in a reducing atmosphere to partly devolatize it, remove all moisture, and remove the pyritic type of sulfur is an object common to both processes disclosed herein.

Slight oxidation to destroy the agglomerating tendencies of those coals which tend to fuse upon heating does not appear to hinder subsequent removal of the sulfur, and it is intended now to accomplish this prior to treatment with hydrogen.

Treating hydrocarbonaceous materials with hydrogen along at elevated temperature, i.e., 1400 to 1600 F. and elevated pressure tends to remove sulfur, but in so doing it, significant amounts of carbon are removed. An object of this invention is to treat the coal in a multi-stage contactor, after partial devolatization and desulfurization, with a hot hydrogen stream to which methane has been added. The methane inhibits the reaction of the carbon with the hydrogen without effecting the desulfurization step and is derived from the partial devolatization of coal.

These and other objects will be apparent from the following specification and drawings, in which:

FIG. 1 is a flow diagram for one example of the process;

FIG. 2 is a view similar to FIG. 1, but showing a modification; and

FIG. 3 is a diagrammatic showing of a multi-stage contactor.

Referring now to the drawings, in which like reference numerals denote similar elements, the starting material, for example, bituminous coal sized to "/z by zero, dried and pre-heated, is fed into a fluid bed reactor for complete drying and light heat treatment at from 700 to 800 F. to prevent subsequent agglomeration in the multistage contactor. In the fluid bed reactor, partial devolatilization occurs and some sulfur, particularly the pyritic type, is removed. It is essential that the hot gas feed as indicated at 6 to the fluid bed reactor be oxygen free as possible so as to provide a reducing atmosphere in the reactor. These are recycle gases from the remainder of the system consisting essentially of hydrogen and methane. Only enough air is added to provide heat via a partial combustion which is required to heat and maintain the bed at temperature. Accordingly, the fluidized bed remains in a reducing atmosphere. The gases exhausted as indicated at 8 from the fluid bed reactor can be utilized for combustion or, as in the case of the FIG. 2 example, recycled through the recovery system.

From fluid bed reactor 2 the coal, then char, is fed as indicated by the feed line 10 into a multi-stage contactor 12. About of the coal input to fluid bed reactor 2 is reported into the char entering multistage contactor 12.

A multi-stage contactor 12 is diagrammatically shown in FIG. 3. It consists of an enclosure 13 hearing a hopper input 14 through which the char is deposited upon a perforated endless belt 16 which runs over sprockets 18 at each end of the enclosure. The char is spread to form a bed 20 by means of a spreader gate 22. Beneath the upper belt run is a zoned airbox with at least six zones 25 having individual gas input pipes 26. Over the upper belt run are partitions 28 which cooperate with the airbox zones to form individual plenum chambers. Pipes 30 exhaust the gases from between the partitions 28. After being treated in contactor 12, the desulfurized char drops off the end of the belt run into an outlet 32.

Treatment of the coal in the multi-sage contactor is differentiated from the treatment in the fluid bed reactor in that in the contactor the bed remains static while being exposed to the hydrogen containing gases. In effect, each zone becomes a separate reactor wherein the temperature may be varied as desired. The contactor is operated at elevated temperatures (i.e., 1000 to 1700" F.) and elevated pressures, 14.7 to 500 p.s.i.a. which could result from placing a compressor in line 44 before preheater. The temperatures are maintained by the exo-thermic reactions of carbon with small amounts of oxygen and carbon monoxide that appear in the gases or are introduced into the gases. The incoming hydrogen containing gas is essentially H 8 free and within the contactor, the ratio of H 5 to H is held at less than 1 to parts. If needed, a small amount of air may be introduced into the incoming gas line as indicated at 31 so as to produce sufficient reactions in the individual plenum chambers within the contactor as to maintain the desired elevated temperatures, or the air may be fed individually to the airbox zones in controlled amounts. An added benefit to the treatment in the multi-stage contactor is that the coal is continuously devolatilized thermally, thereby adding H and methane to the exhausted gas and providing the capacity for further sulfur removal. All hydrogen produced within the process is by thermal devolatilization.

The volume of hydrogen containing gas required for desulfurization in the multi-stage contactor may be very substantially reduced by adding a H S acceptor to the char fed to the contactor. Acceptor Technology has been described by others. This may be preferred because it simplifies gas handling and the gas cleanup facilities. It has been demonstrated that the quantities of hydrogen needed in the presence of an acceptor, such calcined dolomite, is only one to two times stoichiometric. The quantity of an acceptor required with hydrogen is also one to two times stoichiometric. While regeneration and recycle of the acceptor is not a simple matter, it can be accomplished with known equipment.

The char infed to multi-stage contactor 12 produces more hydrogen than is lost by reaction or leakage; therefore, gas containing hydrogen, methane, and CO is continuously withdrawn through output line 34 from the contactor. This gas is low in -B.t.u. value (100-250), but it may be burned for its heating value. The contactor has the capability of providing the residence time that enables operation at lower pressures and temperatures and the recycle of large volumes of gases. The coal used to illustrate the concept of desulfurization is presented in Table I. The char from the fluidized bed reactor prior to entry of the multi-stage contactor and after the multi-stage contactor is also shown in Table I.

TABLE I.COMPOSITION OF COAL AND CHAR Composition (dry, wt. Char from Char from percent) Coal (Ill. #6) fluidized bed dcsulfurizer 17. 73 20. 42 24. 11 44. 08 50. 77 66. 95 38. 19 28. 79 8. 94 Sulfur 4. 20 4.00 1. 20

The above case represents about 70% by weight recovery of the input coal as char. Residence time in the contactor should be about 120 minutes. The processing conditions in the multi-stage contactor for these results needs to be from 1000" to 1700 F., with the temperature increasing by about 200 F. during passage over each of the zones of the airbox until from 1600 to 1700 F. is reached and there is obtained a hydrogen partial pressure of about one atmosphere. Under these conditions, Illinois #6 seam test coal is about 75% to 80% desulfurized. Retention time of less than 120 minutes will result in less sulfur removal. If hydrogen partial pressure is increased to atmospheres, 75% to 80% desulfurization may be accomplished in a shorter length of time. It has been determined, however, that coals with higher percentages of the organic sulfur are more difiicult to desulfurize and an H 8 acceptor has to be utilized if the sulfur is to be reduced to less than one percent in the desulfurized char.

The gas is withdrawn from multi-stage contactor through outlet pipes 30 and common outlet line 34, essentially hydrogen, methane and CO are fed through a tar removal and clean-up apparatus 36, thence to a compressor 38, thence to H 8 removal apparatus 40 from which sulfur can be removed for disposal. Excess gas from H S removal apparatus can be withdrawn for combustion as indicated at 42 and the remainder is recycled through recycle gas heater 46. From heater 46 the steam is split, some being recycled back to fluid bed reactor 2, and the other being fed via line 48 back into multi-stage contactor 12.

The process diagrammed in FIG. 2 is essentially the same as that of FIG. 1, except that the exhaust gases from fluid bed reactor 2 are recycled as indicated by line 50 into a tar removal and clean-up apparatus 36. In both instances, the tar is fed as indicated at 52 to the recycle gas heater 46 and used as fuel.

4 Whereas about 20% to 40% of the volatiles in the coal and about 10% of the sulfur is removed in the form of H 8 and small amounts of S0 in the fluid bed reactor, about 30% to 50% of the volatiles in the original coal are removed in the multi-stage contactor, so that the desulfurized char is essentially devolatilized. It has a maximum of 10% to 12% volatiles. This is reflected by the fact that the gases withdrawn from multi-stage reactor 12 have about 35% H by volume and about 12% CH We claim: 1. A process for removing sulfur from raw coal, which comprises oharring the coal in a reducing atmosphere within a fluid bed reactor at a temperature of from 700 to 800 F. until some sulfur, essentially pyritic sulfur and some volatile matter originally in the coal are driven off, then transporting the charred coal in static bed form through a confined atmosphere while sweeping a stream of hot hydrogen and methane through the charred coal and while feeding air thereto in sufficient quantity to promote limited combustion suflicient to raise the temperature thereof gradually from the temperature achieved in the fluid bed reactor to about 1700 F. and thereby driving off the char volatile matter and sulfur remaining thereinafter.

2. The method recited in claim 1, wherein a gas pressure of from 14.7 to 500 p.s.i.a. is maintained in the confined atmosphere.

3. The method recited in claim 1, wherein the sweep gas is passed through a closed circuit system from the confined atmosphere through tar and sulfur removing apparatus and thence through a heater back to the confined atmosphere.

4. The method recited in claim 3, wherein some gases derived from the heater are fed through the coal in the fluid bed reactor.

5. The method recited in claim 4, wherein the char is maintained in the confined atmosphere sufficiently long as to extract from the coal hydrogen and methane in excess of system losses.

6. The method recited in claim 4, wherein exhaust gases from the fluid bed reactor are returned to the system prior to tar recovery and sulfur removal.

References Cited UNITED STATES PATENTS 3,251,751 5/1966 Lindahl et a1. 201-17 X 2,717,868 9/1955 Gorin et al 201-17 3,640,162 2/ 1972 Lee et a1. 44-1 R 2,700,592 1/1955 Heath 23-224 CARL F. DEES, Primary Examiner US. Cl. X.R. 

